Torque transmitting devices

ABSTRACT

A torque transmission device consists of a resilient coupling between two shafts. The resilient coupling comprises an assembly mounted on one shaft and provided with a plurality of cylinders each having a piston and a cam arrangement mounted on the other shaft and controlling the piston as regards movement in their respective cylinders upon angular displacement between the two shafts under load conditions. A fluid-filled passage connects the cylinder heads with an outlet for indication or control purposes. The cylinders may be arranged radially with respect to the shaft axes or parallel thereto. A suitable indicating instrument may be connected to the outlet for torque sensing and the device may also be used for torque limiting by connecting to the outlet, means, for instance a metallic bellows, which, at a predetermined value of fluid pressure, increase the volume occupied by the fluid. In addition, the device may be used as a fluid clutch by the provision of manually-operated means for increasing the volume occupied by the fluid.

United States Patent Blake et a1.

[54] TORQUE TRANSMITTING DEVICES Allspeeds Holdings Limited, Accrington,Lancashire, England [22] Filed: Feb.18,1970

[21] Appl.No.: 12,383

[73] Assignee:

[30] Foreign Application Priority Data Feb. 18, 1969 Great Britain..8,807/69 [52] U.S. C1. ..192/56 F, 73/136 D, 192/59, 192/60 [51] Int.Cl ..Fl6d 43/20, F16d 31/02 [58] Field of Search 192/56 F, 59, 85 A, 60;73/136 R, 136 D; 91/499; 64/29; 81/524, 52.5; 92/101 [56] ReferencesCited UNITED STATES PATENTS 2,244,185 6/1941 Bakewell ..8l/52.5 UX2,408,501 10/1946 Wright 2,597,514 5/1952 Nash 3,108,471 10/1963 Bucheleet a1 2,546,062 3/1951 Ernst 3,274,896 9/1966 Terho 3,419,117 12/1968Conway 3,527,329 9/1970 Jordan 192/85 A [451 May 23, 1972 PrimaryExaminer-Allan D. l-lerrmann Atrorney-Youn g & Thompson [57] ABSTRACT Atorque transmission device consists of a resilient coupling between twoshafts. The resilient coupling comprises an assembly mounted on oneshaft and provided with a plurality of cylinders each having a pistonand a cam arrangement mounted on the other shaft and controlling thepiston as regards movement in their respective cylinders upon angulardisplacement between the two shafts under load conditions. Afluid-filled passage connects the cylinder heads with an outlet forindication or control purposes. The cylinders may be arranged radiallywith respect to the shaft axes or parallel thereto. A suitableindicating instrument may be connected to the outlet for torque sensingand the device may also be used for torque limiting by connecting to theoutlet, means, for instance a metallic bellows, which, at apredetermined value of fluid pressure, increase the volume occupied bythe fluid. In addition, the device may be used as a fluid clutch by theprovision of manually-operated means for increasing the volume occupiedby the fluid.

10 Claims, 8 Drawing Figures TORQUE TRANSMITTING DEVICES The presentinvention relates to a torque transmission device which is capable of anumber of different applications, such as, for example, to torquesensing, to torque limiting and to fluid clutches.

Torque transmission devices are well known and in their application totorque sensing usually consist of a fluid-filled coupling having adegree of flexibility, the coupling being arranged between a driving anda driven shaft. Different tvpes of coupling have been proposed, some ofwhich are of considerable complexity and consequent high cost.

The object of the present invention is to provide a torque transmissiondevice which is not only efficient in operation but in which thecoupling is of comparatively simple and robust construction.

According to the invention, in a torque transmission device havingresilient coupling means responsive to angular displacement between afirst and a second shaft under load conditions for giving an indicationof applied torque the coupling means comprises an assembly provided withone or more cylinders having or each having a piston, the assembly beingattached to said first shaft and a cam arrangement attached to saidsecond shaft and controlling the piston or pistons as regards movementin the or their respective cylinders upon angular displacement betweenthe two shafts, a fluid-filled passage in the assembly connecting thecylinder head or heads with an output for indication or controlpurposes.

The invention will be better understood from the following descriptionof a number of embodiments taken in conjunction with the accompanyingdrawings comprising FIGS. 1-8. Of the drawings FIG. 1 shows apart-sectional view of one embodiment of the torque transmission devicealong the line A-A of FIG. 2, in which the cylinders are arrangedradially with respect to the axes of the driving and driven shafts,

FIG. 2 shows a part-sectional end elevation of the device along the lineC-C of FIG. 1, 7

FIG. 3 shows a sectional view of a detail of the device,

FIG. 4 shows a part-sectional view of another embodiment of the devicein which the cylinders are arranged parallel to the axes of the drivingand driven shafts,

FIG. 5 shows in part the configuration of the cam arrangement employedin the embodiment of FIG. 4,

FIG. 6 shows a further embodiment of the invention in which thecylinders are arranged parallel to the axes of the driving and drivenshafts and in addition the driving shaft extends within a hollow drivenshaft.

FIG. 7 shows control means employed when the device is to be used fortorque limitation purposes, and

FIG. 8 shows control means employed when the device is to be used as afluid clutch.

Referring now to the drawings and more particularly to FIGS. 1 and 2,the torque transmission device comprises a circular outer coverconsisting of an end cover 9 and a housing 10, the casing havingcircular recesses 11 and 12 at each end for the reception of bearingsfor the driving and driven shafts. The driving shaft 13 is carried inbearings 14 and 15 in the recess 11 and is provided with a ring mounting16 to which the cylinder assembly 17 is secured by bolts 18 of whichonly one is visible in the drawing. Thecylinder assembly consists of acircular block 19 provided with three cylinders 20, 21 and 22 arrangedradially of the driving shaft at angles of 120 about the axis of thedriving shaft. The cylinders are each provided with pistons 23, 24 and25 and the inner end of each piston is formed with a recess 26 as shownfor cylinder 23. The part of the piston left after forming the recess 26is drilled to receive a spindle 27 on which is mounted an anti-frictionroller 28, the rollers 29 and 30 for the pistons 24 and 25 being shownin FIG. 2.

The driven shaft 31 is mounted in bearings 32 and 33 in the recess 12and has attached to it a circular member 34 which is located within acircular aperture 35 in the block 19 and the recesses 26 of the pistons23, 24 and 25. The member 34 is provided with a peripheral cam track 36in which the rollers 28, 29 and 30 engage. The cam track has threeinwardly extending depressions 37, 38 and 39 (FIG. 2) arranged at anglesof and under no-load conditions the rollers are positioned in the rootsof the depressions as shown in FIG. 2.

The head of cylinder 20 is connected through an L-shaped duct 40 to acircular recess 41 in the block 19, the heads of the other two cylindersbeing similarly connected to recess 41. An annulus 42 seats within therecess 41, partially filling the recess and the annulus is provided withthree longitudinal ducts at 120 separation, one for each cylinder, theduct 43 associated with cylinder 20 only being shown. The annulus 42 isheld against rotation within the recess bv three pins located in boresin the annulus and the recess. The bores are arranged with 120separation and are offset with respect to the ducts 43. One pin 60 isshown in FIG. 1. The three longitudinal ducts terminate in an annularchannel 44 formed in the other face of the annulus. This outer face ofthe annulus engages with a further annulus 45 located within a recess 46in the end cover 9. Annulus 45 is also provided with three longitudinalducts at 120 separation, duct 47 only being shown. A circular channel 48coterminous with annulus 45 is provided in the end cover 9 and a duct 49opens into the channel 48 and extends to the outside of the end cover 9.The cylinder heads and the various ducts and channels are filled with asuitable fluid and a pressure-operated indicator 50 having a gaugecalibrated in torque units is connected to the outer end of duct 49.Alternatively the outer end of duct 49 may be connected to externalcontrol equipment.

In operation under no-load conditions, the driving shaft 13 is rotatedand with it the block 19 comprising the cylinder as sembly. Under theseconditions, there is no tendency for the rollers 28, 29 and 30 to riseup the sides of the depressions 37 38 and 39 respectively in the camtrack, and the circular member 34 and hence the driven shaft 31 arerotated with the driving shaft as a single unit, there beingsubstantially no increase in the fluid pressure. When a load is appliedto the driven shaft 31, there will be a tendency for a small relativemovement to take place between the driving and driven shaft due to thetorque applied to the driven shaft. The rollers at the piston ends willtherefore ride up one side of the depressions in the cam track and thepistons will move outwardly in the cylinders. This will decrease thevolume of the space occupied by the fluid in proportion to the appliedtorque and consequently increase the pressure in the fluid, also inproportion to the applied torque. This increase will be indicated by thepressure-operated indicator 50. It will be understood that effectivelythe device converts an applied torque into a thrust proportional to theapplied torque and it is the thrust that gives the indication of thetorque.

It will be appreciated from the foregoing description that there will berelative movement between the annuli 42 and 45 at the engaging facesthereof and there is therefore a possibility of a fluid leak here. Thisis overcome by spring-loading the outer face of annulus 42 against theouter face of annulus 45 as shown in FIG. 3. The annulus 42 is providedon its inner face with three recesses with 120 separation and offsetwith respect to the ducts 43, one recess 51 being shown in FIG. 3. Ahelical spring 52 is located between the base of the recess 51 and thebase of the recess 41 in which the annulus 43 is positioned.Additionally the opposing faces of the annuli have a lapped finish.Leakage longitudinally of the annuli is prevented by the provision of 0"rings 53, 54, 55 and 56. The annulus 42 is made of brass or bronze andthe annulus 45 of hardened steel. The only other possibility of fluidleakage is between the cylinder bores 20, 21 and 22 andthe respectivepistons 23, 24 and 25 and this is prevented by closing the outer ends'ofthe cylinders with a diaphragm 57, preferably made of rubber. The block19 is formed in two parts and the lower part is provided with a circularrecess 58 for the reception of a peripheral flange 59 on the diaphragm,the latter being kept in place by the securing of the upper part to thelower part. With these arrangements the possibility of fluid leakage toan extent which reduces the accuracy of the device is prevented.

The embodiment shown in FIG. 4 of the drawings is similar to that shownin FIG. 1 but is of more compact construction in that the cylinders arearranged parallel to the axes of the shafts instead of radially as inFIG. 1. In view of the similarity between the two embodiments, the sameparts are given the same references in FIGS. 1 and 4.

Referring now to FIG. 4, the driving shaft 13 is carried in bearings 14and 15 in the recess 11 and the cylinder assembly 17 is bolted by bolts80 to the end of the driving shaft so that the assembly engages with anannular ring 81, fixed to the driving shaft. The cylinder assemblyconsists of a block 19 provided with three cylinders arranged with theiraxes parallel to the driving shaft, the cylinders being arranged at 120separation about the axis of the driving shaft. Only one of thecylinders, 20, is shown in FIG. 4, the other two being arrangedsimilarly to those shown in FIG. 2 of the previously describedembodiment. The cylinders are each provided with pistons, such as piston23 in cylinder 20, and the right-hand end of each piston is providedwith a slot 82 for the reception of an anti-friction roller 83. Thelatter is maintained in position by providing a transverse hole 84 atright angles to the slot 82, the hole receiving an insert 85 throughwhich screw 86 passes into a threaded hole in the center of the boss ofthe roller.

The driven shaft 31 is mounted in bearings 32 and 33 in the recess 12and has keyed to it the circular member 87 which is provided with a facecam 88 engaging with the anti-friction rollers as shown in FIG. 5 forroller 83. The face cam has three inwardly extending depressionsarranged at angles of 120 about the axis of the driven shaft and underno-load conditions, the rollers are positioned in the roots of thedepressions.

The outer end of each of the cylinders is again closed by a diaphragm57, preferably of rubber, secured in position in a similar way to thatshown in FIG. 1. Each cylinder head is again connected by an L-shapedduct 40 to a recess 41 which houses the annulus 42. The annulus 42 hasthree longitudinal ducts at 120 separation, one for each cylinder, theduct 43 for cylinder only being shown. The three longitudinal ductsterminate in an annular channel 44 in the outer face of the annulus. Theannulus 42 is maintained against rotation within the recess in the sameway as that shown in FIG. 1. The outer face of the annulus 42 engageswith a second annulus 45 located within recess 46 in the end cover 9,the annulus 42 being spring-urged against annulus 45 in the mannerdescribed with reference to FIG. 1. Annulus 45 is also provided withthree longitudinal ducts at 120 separation about the axis of the drivingshaft, duct 47 onlv being shown. A circular channel 48 coterminous withannulus 45 is provided in the end cover 9 and a duct 49 opens into achannel 48 and extends to the outside of the end cover. The cylinderheads and the various ducts are again filled with a suitable fluid andan indicator or control equipment is connected to the outer end of duct49.

It will be understood that with the axial arrangement of the cylinders,there will be a thrust between the driving and driven shafts whichnecessitates the provision of a thrust bearing 89 between the twoshafts.

The device shown in FIG. 4 operates in a similar manner to thatdescribed with reference to the embodiment of FIG. 1. That is, underno-load conditions, the driving and driven shafts rotate as a singleunit, the anti-friction rollers remaining in the roots of thedepressions in the cam face. When a load is applied to the driven shaft,the rollers will ride up one side of the depressions in the cam face andthe pistons will move towards the left as shown in the drawing toincrease the pressure in the fluid in proportion to the applied torque.This increase will be indicated by the indicator connected to duct 49 orwill exert a control of whatever equipment is connected to the duct.

A further embodiment of the invention is shown in FIG. 6 which issimilar to FIG. 4 in that the pistons are arranged with their axesparallel to the axis of the shafts. However, in this embodiment thecoaxial driving and driven shafts are arranged one within the other togive an even more compact construction than that shown in FIG. 4. Thisembodiment is particularly suitable for use in transmitting a drivefrom, for example,

a motor. In view of the similarity between the embodiments shown inFIGS. 4 and 6, the same parts are given the same references in the twodrawings.

Referring now to FIG. 6, the driving shaft 13 is hollow and is mountedon the motor shaft (not shown) on which it fits. The outer casing issupported on the driving shaft 13 by the bearing 32 and the hollowdriven shaft 31 is supported on the driving shaft by bearings 70 and 71.The cylinder assembly 19 is keyed on to the driving shaft 13 and thecylinders are arranged parallel to the axes of the shafts. As in FIG. 1,only one cylinder, 20, is shown in FIG. 6, the other two cylinders beingarranged at 120 with respect to cylinder 20 in the manner shown in FIG.2. The cam arrangement takes the form of a face cam 72 which has thesame configuration as the face cam 88 shown in FIG. 5, the rollers 83resting in the no-load condition in the roots of the depressions in theface cam.

The outer end of each of the cylinders is again closed by a diaphragm57, preferably of rubber, secured in position in a similar way as thatshown in FIG. 1. Each cylinder head is again connected by an L-shapedduct 40 to a recess 41 which houses the annulus 42. The annulus 42 hasthree longitudinal ducts at 120 separation, one for each cylinder, theduct 43 associated with cylinder 20 only being shown. The threelongitudinal ducts terminate in an annular channel 44 in the outer faceof the annulus. The annulus 42 is maintained against rotation within therecess in the same way as that shown in FIG. 1. The outer face of theannulus 42 engages with a second annulus 45 located within recess 46 inthe outer casing 10, the annulus 42 being spring-urged against annulus45 in the manner described with reference to FIG. 1. Annulus 45 is alsoprovided with three longitudinal ducts at 120 separation, duct 47 onlybeing shown. A circular channel 48 coterminous with annulus 45 isprovided in the casing and a duct 49 opens into channel 48 and extendsto the outside of the casing. The cylinder heads and the various ductsand channels are filled with a suitable fluid and an indicator orcontrol equipment is connected to the outer end of duct 49. A thrustbearing 89 is again provided between the driving and driven shafts.

The operation of the embodiment shown in FIG. 6 is the same as thatdescribed relative to FIGS. 1 and 4 and no further description of theoperation is thought to be necessary.

When the device described is provided with an indicator calibrated intorque units, it operates as a torque sensing device. It can, however,easily be adapted to a torque limiting device by the provision of meanswhich, at a predetermined value of the fluid pressure, operate toincrease the volume occupied by the fluid and hence reduce the pressure.The reduction in pressure must be such as to enable the rollers at theends of the cylinders to rise out of the depressions in the camarrangement, the drive between the driving and driven shafts being thendisconnected. The cylinder assembly will, of course, continue to rotatebut the rollers at the piston ends will merely follow the outline of thecam arrangement without imparting any drive through the cam arrangementto the driven shaft. The means for pressure reduction could take manyforms and may, for instance, be a relief valve. A preferred form is,however, the arrangement shown in FIG. 7 which incorporates a metallicbellows. Thus referring to FIG. 7, the apparatus shown is for connectionto the duct 49 of any of the embodiments shown in FIGS. 1, 4 and 6, theconnection being made to the bore which connects through duct 101 in thebody 102 to the indicating instrument 50. A branch duct 103 leads to thetorque limiting arrangement. This comprises a cylindrical tube 104having a closure plate 105, a reduced portion 106 of which is providedwith a duct 107 in alignment with the duct 103. A metallic bellows 108is secured, for instance by soldering, to the inner face of the closureplate 105, the other end of the bellows being similarly secured tomember 109 which is slidable within the bore of the tube. A splitcylinder 110 is provided in the bore of the tube between the plate andthe member 109. A closure cap 111 is provided at the other end of thetube, the cap being internally threaded to co-operate with an externallythreaded portion of the tube. A calibrated helical spring 1 12 islocated in the space between the slidable member 109 and the inner faceof the closure cap.

in operation, the spring 112 exerts a pressure against the slidablemember 109 and in the no-load condition this pressure is sufficient tomaintain the slidable member in the position shown in the drawing,compression of the bellows being restricted by the cylinder 110. Underload conditions, the pressure within the bellows increases and when thispressure exceeds that exerted by the spring 112, the slidable member 109moves to the right. The bellows thereupon expands and increases thevolume occupied by the fluid. The rollers at the ends of the cylindersthereupon rise out of the depressions in the cam arrangement and thedrive between the driving and driven shafts is disconnected.

It will be understood that the pressure exerted by spring 112 on theslidable member 109 may be varied by screwing the closure cap 111 eitherinwardly or outwardly and micrometer type scales 113 and 114 areprovided on the outer surface of the tube 104 and the edge of theclosure cap 1 11 to enable accurate setting of the limiting torque.

The feature of torque limitation can also be adapted to provide a fluidclutch by the addition of the control means shown in FIG. 8 which servesto vary the volume occupied by the fluid and hence the fluid pressure.This consists of a casing'90 having an inlet 91 which is connected tothe duct 49 (FIG. 1), an outlet 92 which is connected to apressure-operated indicator and a fluid reservoir 93 in communicationwith the inlet 91 and outlet 92. The fluid reservoir 93 is closed by aplug 94 carried by an internally threaded cylindrical closure 95 whichis screwed on to the externally threaded casing 90, fluid seals 96 and97 preventing any fluid leakage from the reservoir past the plug. itwill be appreciated that unscrewing the plug from the reservoir willincrease the volume occupied by the fluid and a point will be reachedwhere the rollers ride out of the depressions in the cam arrangement dueto the decrease of pressure in the fluid and as previously described thedrive between the driving and driven shafts is disconnected. A clutchingaction is thereby obtained. Preferably the scale of the indicatorconnected to outlet 92 has an adjustable distinctive marking to indicatethe limiting torque.

it will, of course, be understood that the device shown in FIG. 8 maytake other forms. For instance, the plug may be lever operated betweentwo positions or may be pedaloperated although in both these cases itmay be desirable in view of the small movement required by the plug tointroduce some form of reduction gear.

The previously described embodiments are given by way of example onlyand many modifications may be made by those skilled in the art withoutdeparting from the invention. Thus although a single cylinder could beused, this would involve balancing the block and the use of threecylinders as shown is obviously more satisfactory. However, a numberother than three could also be used. It will also be understood thatincreasing the number of cylinders would amplify the pressure increasefor a given rise of the rollers out of the depressions on the cam plate.It is therefore possible to design a standard cylinder and piston and touse different numbers of these in accordance with the type of apparatusrequired. However, it will be understood that the design of atransmission device to fit a particular specification may requirecylinders other than such standard cylinders. Furthermore, the devicehas a design flexibility in other respects because, within practicallimits, the dimensions may be varied at will.

One of the important advantages of the device disclosed in FIGS. 1, 4and 6 is the fact that there is minimum contact between the fluid andthe stationary casing 10. This as previously mentioned only occurs whereduct 44 annuli 42 and 45 engage and the described arrangements of thesetwo annuli are sufficient to prevent fluid leakage to an extent whichwould reduce the accuracy of the device.

It will be understood that the limiting torque and clutch aspects of theinvention have very valuable application to automatic control systems ofthe sequencing type in which case the necessary reduction in fluidpressure would be controlled by a suitable valve or like device.

We claim:

1. A torque transmission device comprising a casing, a first and asecond shaftvmounted in axial alignment in said casing, an assemblyattached to said first shaft and provided with a plurality of cylindersfor the reception of liquid, a piston in each of said cylinders, a camarrangement attached to said second shaft arranged to effectsimultaneous and similar movement of the pistons in the cylinders onrelative rotation between the two shafts, an outlet in said casing, apassage connecting all the cylinder heads with said outlet, andyieldable means attached to said outlet for confining said liquid in anenclosure of variable volume.

2. A torque transmission device as claimed in claim 1, and meansresponsive to enlargement of said enclosure for disconnecting the drivebetween said first and second shafts.

3. A torque transmission device as claimed in claim 2, the

last-named means comprising a metallic bellows connected to said outletand spring means acting on said bellows to prevent expansion thereofuntil a predetermined increase in the fluid pressure occurs.

4. A torque transmission device as claimed in claim 3, and means foradjusting the pressure exerted on the bellows by said spring meansthereby enabling the value of the limiting torque to be varied.

5. A torque transmission device as claimed in claim 1, said cylindersbeing equally spaced about the axes of the shafts.

6. A torque transmission device as claimed in claim 1, wherein aplurality of cylinders is formed in said assembly, the cylinder axesbeing radial with respect to the axes of the shafts.

7. A torque transmission device as claimed in claim 6, wherein the camarrangement consists of a cam track provided in a member secured to saidsecond shaft, the pistons being provided with anti-friction rollerswhich under no-load conditions engage in the roots of inwardly extendingdepressions in the cam track.

8. A torque transmission device as claimed in claim I, wherein aplurality of cylinders is formed in said assembly, the cylinder axesbeing parallel to the axes of the shafts.

9. A torque transmission device as claimed in claim 8, wherein the camarrangement consists of a face cam provided on a member secured to saidsecond shaft, the pistons being provided with anti-friction rollerswhich under no-load conditions engage in the roots of depression in theface cam which extend away from the pistons.

10. A torque transmitting device comprising a first shaft, a

second shaft in axial alignment with said first shaft, an assemblyattached to said first shaft, a plurality of cylinders in said assemblyequally spaced around the axes of said shafts, a piston in each of saidcylinders, an outlet, yieldable means connected to said outlet forconfining said liquid in an enclosure of variable volume, aliquid-filled passage connecting said cylinders with said outlet therebyto form an internally closed system for the liquid and a cam arrangementattached to said second shaft, the cam arrangement under load conditionseffecting simultaneous and similar movement of the pistons in thecylinders and movement of the liquid through said outlet until thepressure exerted by the liquid on the yieldable means balances thetorque applied to said second shaft whereupon a direct drive obtainsbetween said first and second shafts.

'l *0 I l I!

1. A torque transmission device comprising a casing, a first and asecond shaft mounted in axial alignment in said casing, an assemblyattached to said first shaft and provided with a plurality of cylindersfor the reception of liquid, a piston in each of said cylinders, a camarrangement attached to said second shaft arranged to effectsimultaneous and similar movement of the pistons in the cylinders onrelative rotation between the two shafts, an outlet in said casing, apassage connecting all the cylinder heads with said outlet, andyieldable means attached to said outlet for confining said liquid in anenclosure of variable volume.
 2. A torque transmission device as claimedin claim 1, and means responsive to enlargement of said enclosure fordisconnecting the drive between said first and second shafts.
 3. Atorque transmission device as claimed in claim 2, the last-named meanscomprising a metallic bellows connected to said outlet and spring meansacting on said bellows to prevent expansion thereof until apredetermined increase in the fluid pressure occurs.
 4. A torquetransmission device as claimed in claim 3, and means for adjusting thepressure exerted on the bellows by said spring means thereby enablingthe value of the limiting torque to be varied.
 5. A torque transmissiondevice as claimed in claim 1, said cylinders being equally spaced aboutthe axes of the shafts.
 6. A torque transmission device as claimed inclaim 1, wherein a plurality of cylinders is formed in said assembly,the cylinder axes being radial with respect to the axes of the shafts.7. A torque transmission device as claimed in claim 6, wherein the camarrangement consists of a cam track provided in a member secured to saidsecond shaft, the pistons being provided with anti-friction rollerswhich under no-load conditions engage in the roots of inwardly extendingdepressions in the cam track.
 8. A torque transmission device as claimedin claim 1, wherein a plurality of cylinders is formed in said assembly,the cylinder axes being parallel to the axes of the shafts.
 9. A torquetransmission device as claimed in claim 8, wherein the cam arrangementconsists of a face cam provided on a member secured to said secondshaft, the pistons being provided with anti-friction rollers which underno-load conditions engage in the roots of depression in the face camwhich extend away from the pistons.
 10. A torque transmitting devicecomprising a first shaft, a second shaft in axial alignment with saidfirst shaft, an assembly attached to said first shaft, a plurality ofcylinders in said assembly equally spaced around the axes of saidshafts, a piston in each of said cylinders, an outlet, yieldable meansconnected to said outlet for confining said liquid in an enclosure ofvariable volume, a liquid-filled passage connecting said cylinders withsaid outlet thereby to form an internally closed system for the liquidand a cam arrangement attached to said second shaft, the cam arrangementunder load conditions effecting simultaneous and similar movement of thepistons in the cylinders and movement of the liquid through said outletuntil the pressure exerted by the liquid on the yieldable means balancesthe torque applied to said second shaft whereupon a direct drive obtainsbetween said first and second shafts.